Binder for making luminescent screens



Patented Oct. 29,

" a pa atuses.basema amass. r c eatnru i hpni c.1931;

This invention 1 relates binders I for making luminescent screens, thatis to'say, for coating surfaces of vitreous materialgwith a. thin layerI of material adapted to be excited to luminescence 5 by'aetherialradiation, cathoderays, or contact with an electric discharge.

.In the usual process for making luminescent screens, the surface isfirst coated with a thin film of a liquid binder, powdered luminescentmaterial is dusted or sprayed upon this film, and the resulting productis heated to disperse or consolidate the binder.

I y The binders used for this purpose are usually much more viscous thanwater;- among them are glycerine (which may contain additions, especially boric acid), water-glass (i. e. asolution of potassium or sodiumsilicate);, a nd phosphoric or analogous acids in .a solvent such asacetone; many other materials have been proposed, but I have noextensive experience of their use. Of these three glycerine is apt tochar slightly when it is dispersed and to leave behind highly ad- I.sorbent matter (probably carbon) which impairs the efficiency of thescreen. Phosphoric or analogous acids, when they are consolidated,attack the glass; this'is of no consequence when the glass iscomparatively thick, for example the wall of a discharge tube; but ifthe glass is thin, for example the wall of abulb, such as is used 30 forelectric incandescent'lamps, enclosing a highpressure mercury-vapourlamp, the attack makes the glass extremely fragile. The reason may bethe same as that which requires the practice'of double-etchin gin theinternal frosting of such.

3 bulbs. Moreover these acids attack some luminescent materials. Waterglass also weakens the thin glass of a bulb very greatly; but-it is notknown whether the reasonis the same.

The primary object of the invention is to provide a binder, suited forcoating thin bulbs, which is relatively free from all. thesedisadvantages. Itis also desirable that it should have a property notpossessed fully by any of the three materials mentioned, namely that theresidue left' by its dispersal or consolidation should be easily solublemay be aqueous of certain stable inorganic salts was? cam raman;PinirerfEngland, v =2 aitlior to'General Electric qoinlie iy, a corporaof @the alkali. metals provide" binders having in a large degree thepde'siredfproperties. {,By stabl'e! -I mean that in the consolidation[stage ofthe' process, the salts undergo no chemical change either bywayof decomposition 'or by way of reaction with the glass or luminescentmaterial. By

anon-viscous solution l mean onewhich' is not substantiallymoreviscousthan water. The remarkable discoveryon which e inventionrests is that a satisfactory binder ca is 'neltherviscous, norsuifers anhange other than loss of solvent. However it must be observed that thesebindershavehot fully one of the desired properties, for they are-liableto attack luminescent sulphides. f 1

' 1 According to the invention in the manufacture of luminescent screens(other than those in which a sulphide is the main luminescent material)bythe aforesaid usual-process the temperature attained in the third orheating step of' a" l the said process does not exceed 500 C. and thebinder consists substantially of ,a non-viscous solution of one or moreinorganic salts of the alkalimetals, which salts are such that theyundergono chemical change when heated in the 25 third step of the saidprocess.

Many such salts have been examined; those that have proved mostsatisfactory are sodium or potassium carbonate or sulphate. The'solutionshould preferably contain about 10% 'of the so carbonate or 5% of thesulphate, the solvent being water. One embodiment of the invention willnow be 1 described by way of example. A thoroughly clean bulb, such, asis used for 1500 watt electricina candescent lamps, is partially filledwith a'10% pgueous solution of sodium carbonate (NazCOalOI-BO)cent-screen other than one in which'a sulphide 60 v is the mainluminescent material which com: prises attaching the'luminescentmaterial to a support member by means of a binder consisting of a .nonvisc'ous solution, of an'inorganic salt of the class consisting of thecarbonates and 56 bicfound which not exceeding 500 C. I

, tion of, an 5 inorganic salt of the class consisting 'ofcarbonatesfan'd, sulphates of and potassium, dusting the powdered luminescentmaterial upon the said film, and then heating to a temperature notexceeding 500 C.

4.,A- luminescent' screen. .other than .one in sulphates of alkalimetals, and then heating to a temperature not exceeding 500 ,C. l

' 2.. The method of manufacturing a luminescent screen "other tha'ncnein whichasulphideis the g main luminescent material which comprisescoatwhich a sulphidefis themain luminescent mate- I ing the surface of asupport member with a thin rial comprising a support rhmbercoz'zted witha. film of a binder consisting of anon-viscous solu-, binder consistingof an inorganic salt ofthe class tion of an inorganic salt of the classconsisting consisting of the carbonates and sulphates of of thecarbonates and sulphates of alkalfmetalss '"all:ali-imetals; andpowdered luminescent material 10 the said film, and then heating teatemperature,

dusting the powdered luminescent material upon adherent to said binder.10

a 5, A luminescent screen other than one in ewhi chaisulphide is themain luminescent mate- 3; The method of manufacturing a luminescentscreen other than one in which asulphide is the ria1 comprising;afsupport member coated with g I V a binder consisting of an inorganicsalt of the main luminescent material whichfcomprises pat;- 1a sqconsisting of the carbonates and sulphates ll ing the surface of asupport member with a'thin of s'odiumand potassium, and powderedluminesfllm of a binder consisting of alnon-viscoussolue cent materialadherent to said binder.

